QUANTITATIVE PROTEOMICS REVEAL OVERALL AMINO ACID TRANSPORT SYSTEMS AND THE RELATED SIGNALING

• Published in: Annals of nutrition and metabolism 2017-10, Vol.71 (Suppl. 2), p.140
• Main Author: Nagamori, Shushi
• Format: Article
• Language: English
• Subjects: Amino acids; Biotechnology; Cancer; Cell proliferation; Leucine; Metabolism; Molecular chains; Nutrient transport; Nutrient uptake; Phosphoproteins; Phosphorylation; Proteins; Proteomics; Rapamycin; Signal transduction; Signaling; Substrates; TOR protein; Transport; Tumor cell lines
• ISSN: 0250-6807; 1421-9697
• DOI: 10.1159/000480486

Amino acids are known as building blocks of proteins and substrates of metabolic and biosynthetic reactions. However amino acids are also recognized as the signaling molecules to regulate cellular metabolism and cell growth. Among amino acids, leucine is the most effective signaling molecule to regulate cell growth and metabolism by activating mechanistic target of rapamycin complex 1 (mTORC1) which is one of the well-recognized cellular signaling pathways mobilized by amino acids. Since leucine is one of essential amino acids, cell needs to take it up from outside by using transporters. It has been reported that Na+-dependent or Na+-independent plasma membrane transporters are able to transport leucine. Normal cells control nutrient uptake and metabolic activities to prevent aberrant cell proliferation. On the other hand, in cancer cells, nutrient transporters are constitutively activated to facilitate the nutrient uptake for robust cell growth. Several studies have reported the overexpression of some amino acid transporters. However, there have been no report about comprehensive expression profile of amino acid transporters in cancer cells due to the problematic nature of transporter proteins. Thus, we have exploited comprehensive and quantitative proteomics to review the functional profiles of amino acid transporters in many cell lines. In our study, we found that cancer cell lines selectively expressed one transporter from each transporter family. Expressions of SLC1A5, LAT1/SLC7A5, SLC7A1 and SLC7A6 were conserved in most cell lines. These results strongly indicate that these transporters are the common transporters to supply amino acids for cancer cells. Of the transporters, LAT1/SLC7A5 transports several large neutral essential amino acids including leucine. By addition of an LAT1-inhibitor BCH, leucine uptake by LAT1 was blocked, and then the phosphorylation of mTORC1 pathway was also suppressed. Therefore, we have applied quantitative phosphoproteomics to analyze the cellular responses to leucine transported via LAT1 comprehensively. Cells were stimulated by leucine in the presence or absence of BCH. Thus, the phosphorylation induced by LAT1-mediated leucine uptake was able to be distinguished. Our result shows that leucine-uptake by LAT1 regulated phosphoproteins involved in multiple cellular processes and revealed the linkage of signaling pathways and cellular responses. These data open a door let us explore the whole picture of signaling stimul